Method of working metals



Patented Apr. 20, 1943 METHOD OF WORKING METALS Rudolf Lowit, Auburn, Maine, assignor to Callite Tungsten Corporation, Union City, N. 1., acorporation of Delaware No Drawing. Application March 6, 1940, Serial No. 322,574=

12 Claims.

This invention relates to novel methods of coating metal surfaces with a carbon layer incident to its working, as well as to novel methods for cleaning the surface particularly of molybdenum, tungsten or their respective alloys.

The present method of making tungsten and molybdenum ductile at room temperature was,

heating, generally below the recrystallization temperature of the metal.

At the present time, .the most extensive use of tungsten is in the form of fine wires for filaments of incandescent lamps and as cathode and heater elements in electronic tubes. Molybdenum wire is used for hooks, supports and grid electrodes. of electronic tubes and for heating elements of electric furnaces. Such wires range in diameter from approximately 1.25 down to 0.03 millimeter. The wire is initially swaged or rolled, generally down to a diameter of about 1.5 millimeters. The final stage in forming the ductile fine wire consists in drawing it through suitable dies to reduce its diameter, in conjunction with suitable heating and annealing operation.

In drawing the wire, there is a drum on which the wire is wound, a graphite lubricant bath for coating the wire, a die, and a second drum driven by suitable motivating means for taking on the drawn wire. A heated zone is arranged about the wire, to suitably heat it prior to its passage through the die. The heating serves to bake the graphite coating onto the wire, and to soften the wire for facilitating its drawing to smaller diameters. The die itself is generally also heated. The ductility of the wire increases with continuous drawing and the wire may eventually be drawn cold in the smallest diameters. The speed of the drawing depends upon the wire diameter. The heat treatment during drawing is such that the wire temperature is kept below the recrystallization point of the metal to prevent embrittlemerit of the wire. Reduction in diameter upon each passage of the wire through the die generally ranges between and per cent.

It is important to have a protective coating on the wire to serve as a lubricant in the drawing to prevent abnormal die wear. This coating also protects the wire surface from oxidation during heating applied in the swaging .as well as the drawing stages of these metals. The protective coating generally used is graphite. The coating has heretofore been applied on the rod, wire or ribbon in the final stage of the swaging and for all the drawing operations by passing it through a bath containing graphite in suspension-or emulsion. Heating bakes the graphite coating on the wire. The graphite coating should preferably be homogeneous in nature for successful commercial results.

Heretofore it has been difiicult to insure a homogeneous coating of this nature on rods or wires "of tungsten and molybdenum. A nonhomogeneous coating results in surface irregularities and abrasion of the drawn wire, as well as in appreciable wear on the die, producing wire' with inferior physical properties. This was due to increased and irregular friction between the die and the wire, resulting in excessive strains in sections of the wire. Commercially, the resultant wires were rejected in substantial measure in their manufacture. The prior surface coating of such wire in their working stages gen erally comprised-besides the graphite, metallic oxides, abraded metal, and other impurities incurred during the successive hot working stages. The resultant layer was non-uniform, and it was heretofore commercially impractical to affix homogeneous coatings in the successive stages;

Several methods were heretofore used to clean the surface of molybdenum and tungsten wire for coating or recoating with graphite during some stage in its working. The coating on such wire with a diameter greater than about one millimeter was in some cases removed by passing the wire through a fused bath of sodium nitrite. However, precaution had to be taken to keep the loss of the pure metal itself to a minimum. In another method tungsten wire was immersed for 30 minutes in boiling sodium or potassium hydroxide, then thoroughly washed with water and finally cleaned with felt pads, A further surface cleaning method was to raise the wire to incandescence in a reducing atmosphere. However, there were the dangers of undesirable effects upon the crystal structure of the metal and the formation of compounds on its surface.

In accordance with my present invention I provide improved methods for cleaning impurities from the surface of molybdenum, tungsten and their alloys, and for uniformly coating such metals 'with a firmly adherent and homogeneous carbon layer to give substantially improved control in their metal working and uniform physical properties in the completed product. Broad ly speaking, one phase of my invention comprises treating such metal with a chemical oxidizer to first loosen all its surface impurities. I have found that a solution containing potassium permanganate is most suitable as such oxidizer. It is to be understood, however, that other suitable oxidizers may instead be used. Upon loosening the surface coating with the oxidizer, the metal is then treated with a. cleaning solvent which does not appreciably attack the pure metthose that are usually hotor their alloys, and secondly, those metals which are usually cold-worked or drawnwith difficulty. Where impurities have been deeply imbedded in the metal surface such as due to prior working,-the metal is preferably first cleaned of its surface impurities in some suitable manner, for example as my my novel cleaning process previously described. Upon cleaning, the

metal is introduced into an oxidizing solution to condition its surface for the subsequent coating of carbon or graphite which homogeneously adheres onto the conditioned surface. I found potassium permanganate solution very suitable as the conditioner for this purpose. When the thus conditioned metal has carbon or graphite applied to it, and is subsequently heated, an adherent layer thereof is baked thereon. When wire is coated in this manner, the carbon ,or graphite layer serves to protect its surface, and to lubricate the drawing action. Other uses for such graphite or carbon layers are indicated, such as in black-body electrodes for radio tubes.

I have found that in some cases it sary to clean or otherwise completely remove the surface impurities from the metal in its working, such as in swaging or wire drawing. The wire with its old or worn graphite coating is treated with the oxidizing or conditioning solution, whereupon the layer thereon is conditioned. When the thus treated wire is then passed through the graphite suspension a resultant homogeneous layer is produced by the new graphite combining with the conditioned old layer.

It is accordingly an object of my present invention to provide a novel method of cleaning surfaces of molybdenum, tungsten or their alloys.

Another object of my present invention is to provide novel methods of removing coatings of graphite and other impurities from molybdenum, tungsten or their alloys.

Still another object of my present invention is to provide novel methods of homogeneously coating metals with a carbon layer.

A further object of my present invention is to provide improved methods of continuously coating :1 wire with a graphite layer.

is unnec- In accordance with one aspect of my present invention, the surface of molybdenum, tungsten or their respective alloys is cleaned of surface impurities with a loosener or oxidizing agent that first loosens the impurities and a subsequent cleaner solution. Surface impurities encountered in working the metal'generally comprises carbon such as graphite from the prior coatings, metallic oxides, abraded metal, and other impurities, The metal, in wire, rod, ribbon or sheet form, is first treated with a solution containing suitable oxidizer. In the case of molybdenum or its alloys with tungsten particularly where molybdenum predominates, I have found that solutions of the halates, perhalates, manganates and permanganates, etc., of the alkali and alkaline earth groups and also the acids of these anions and mixtures thereof are suitable oxidizers for this purpose.- By the alkalies I refer to ammonium, sodium, potas sium, etc. By the alkaline earths I refer to magnesium, calcium, barium,-etc. By the halates I refer tochlorates, bromates and iodates, etc.; and by the perhalates to the perchlorates, perbromates and periodates, etc. In the case of tungsten, I have found that a suitable oxidizing solution is comprised of potassium permanganate 'together with a compound of the class including the oxides, peroxides, hydroxides, cyanides, carbonates, sulphites, sulphides, nitrates, nitrites of the alkali and alkaline earth group. The oxidizing loosener or solution is preferably heated to a temperature below its boiling point. The

metal, when in wire form, may be linearly passed I through the solution, or be arranged in a coil which is then placed therein for any desired period up to one hour or longer.

Treating the molybdenum-or tungsten metal with oxidizing solution, loosens the usual graphitecoating or adhering foreign particles from its surface. The metal may then be rinsed to remove loosened surface particles and excess oxidizing solution. Water may be used for this washing. The loosener or oxidizer undermines the cohesion of the surface impurities on the metal.

The remaining deposits on the metal surface may be completely removed by subjecting the treated metal to a cleaning solution. For molybdenum or its alloys with tungsten, I have found that a cleaning agent suitable for this purpose is amongst the group comprising hydro-v chloric acid, or a solution of halides of the alkali and alkaline earth groups; specifically chlorides, fluorides, bromides and iodides, and the acids of these anions or any combination of these. In the case of tungsten, a suitable clean-v ing agent is one of the class including hydrochloric acid, or oxides, peroxides, hydroxides, cyanides, carbonates, sulphites, sulphides, -nitrates, nitrites of the alkali and alkaline earth groups. Such cleaning agent removes the residual coating and impurities on the metal surface without appreciably attaching or dissolving the metal itself, I prefer to use hydrochloric acid, and have found solutions 5 per cent by weight to the fully concentrated form satisfactory. Concentrated hydrochloric acid is very satisfactory commercially for this purpose for either molybdenum or tungsten or their alloys.

It is to be noted that no evident loss of .metal is en-,

countered in the surface cleaning with my novel process, and that a wire thus cleaned remains uniform in d,iameter.- Since the molybdenum,

tungsten, or their alloys, are not appreciably attacked, the physical characteristics of wire thus cleaned remain intact, being controllable to insure a predetermined uniform diameter.

Heretofore cleaning molybdenum and-tungsten was attempted in a single step with a. relatively strong cleaning agent. tenacious surface impurities encountered on such metals whether or not containing graphite However, the

were generally removed with difliculty by such. 7

single step cleaning due to the irregular character of the impurities. Such strong cleaning agents also appreciably attacked the ,metal sur-. face in portions of least resistance before re.- moving the more resistant impurities. With my two-step cleaning process herein the surface impurities are first converted or loosened onthe metal and then treated with a. cleaning agent which does not appreciably attack the metal itself, giving satisfactory and uniform results.

My invention further contemplates the coating 7 v of metal surfaces with graphite, orvamorphousv carbon in any other form. Such coating is par-z tioularly required in the hot drawing of wires and in some stages of hot rolling or swaging of molybdenum, tungsten and the respective alloys of,

these metals. The graphite coating impedes oxidation of the metal, and in hot drawing serves as a drawing lubricant, protecting the die from ex.-

cessive wear and the wire from damage and undue strain. Metals which are usually colddrawn with difficulty may be similarly treated to advantage. Such metals are those that have compounds formed on their surface which are hard, and difficult to remove, and which increase the die wear, as well as which impart inferior physical characteristics to the drawn .wire.

Stainless steel wire is an example of a metal of.

securing graphite, carbon black, and the like onto the metal surface. I believe that the described conditioners, particularly potassium permanganate, form a deposit which is suspended among the carbo 'n particles and facilitates the flow of the carbon particles during the metal working, particularly in wire drawing.

Where'merely a carbon layer is desired on the metal, such as for use as an electrode element in an electronic tube, carbon black, or carbon in any other form is applied onto the conditioned surface, and preferably heated to firmly bake on thereof with an oxidizer as described hereinabove,

then preferablypartially or completely drying the surface and then coating it with graphite. The

. heating accompanying the working, whether rolling,- swaging or drawlngbakes the graphite layer firmly. thereon. Where; wire is formed by such methods, the conditioned wire is passed through the usual graphite suspension and the heating zone before reaching the rolling or swaging unit or die, and forms a tenacious and homogeneous protective coating thereon. The resultant wire is this class which is cold-drawn. Other metals in I this class are some of the alloys containing chromium, molybdenum, tungsten, tantalum, co-

balt or manganese. In the cold drawing process, the graphite coating does not serve as the'lubricant, but rather acts primarily to protect the die and wire from the effects of the hard surface im- The lubricant used here is the one purities. generally employed in cold drawing.

In accordanie with my invention, the surface of the metal is cleaned of its impurities in any suitable' manner. In the case of molybdenum,

very uniform in physical properties. Due to this homogeneous protective graphite or other coating on the wire, no striations appear thereon, nor does unduetool or die wear take place. The resultant wire is produced with uniform ductility, diameter, tensile strength and elongation throughout its entire length, an important ad- I vantage in commercial production.

The metal surface cleaning and graphite coating processes of my present invention may be practised in various ways, for the different phases of the metal working or wire drawing. The coating of the metal with a protective lubricant layer, such as graphite, may for example be performed in a continuous manner in conjunction tungsten or their alloys,v the surface impurities are advantageously removed by the hereinabove l described two-step process employing an oxidizing solution and cleaning agent solvent. The I clean metal surface is treated with a conditioning solution. Suitable conditioners for this purpose for the hot or cold Worked metals are the loosener agents or oxidizers enumerated hereinabove for the surface cleaning processes of molybdenum, or tungsten. or their alloys. In the case of tungsten, I have found that a potassium pemanganate solution alone also serves as a suitable conditioner when used on a cleaned tungsten surface. In commercial conditioning of. molybdenum, tungsten or their respective alloys, I have found a solution containing potassium'permanganate, for

example between 0.3% to 3.% of potassium penmanganate by weight. very suitable for the surface conditioning. However, other concentrations thereof are feasible.

After partial or complete drying of the conditioned surface, it forms an excellent means for with the rolling, swaging or drawing operations. Wire containing an old or injured graphite coating is .first passed through an oxidizing solution (such as for example the 0.3 to 3.% solution of potassium permanganate by weight referred to above) to act on the old coating and to condition the surface. The wire is then passed through the usual graphite bath, or equivalent compound.

The graphite suspension firmly attaches itself to the conditioned surface of the wire and admixes with the old coating thereon to form a resultant homogeneous graphite layer. In hot working, when the wire is next moved through the usual heating zone, all in a continuous process, the graphite suspension dries on its surface and is baked thereon as an adherent coating. For this continuous procedure the previous intermediate stage for wire cleaning per se is omitted. The

graphite coated wire is then passed through the rolling or swaging unit or die in the usual manner, resulting in a uniform metal product. A coil of wire may be dipped as a whole into the conditioner or oxidizing solution, and subsequently introduced linearly to the continuous process of graphite coating and hot working.

In my novel continuous-procedure of recoating the metal wire, the passage of the wire through myoxidizing solution "or conditioner denum, or their respective alloys. If such metals are annealed with foreign particles on their surfaces, there is great likelihood that the particles would react with the metal and impart undesirable physical properties to the product. I propose to treat the metal or wire to be annealed by the described conditioning treatmentfsuch as with the potassium permanganate, solution, to loosen these particles, and subsequently washing, and also scrubbingc if desired, to remove the foreign particles. The resultant coating is preferably reapplied coating of carbon is loosened and then applying graphite thereon.

5. The method of continuously recoating a carbon coated wire of the class consisting of molybdenum, tungsten, chromium, nickel, iron, cobalt, tantalum and manganese, and their alloys, with a layer of graphite which comprises subjecting the wire to a solution of potassium permanganate and then applying'another layer of the carbon thereon.

6. The method of coating a metal wire of the j group consisting of molybdenum, tungsten, chromium, nickel, iron, cobalt, tantalum and manganese, and their alloys, with a layer of graphite 5 which comprises treating the wire with a solution moved bya cleaning agent such as by hydrochloric acid described, prior to the, annealing stage. I have found that all impurities on the surface of the metal are removed and otherwise rendered inert so that upon subsequent heating or anneal ing in a suitable atmosphere, no chemical action ensues which causes deleterious effects on the metallic surface.

Although I have described preferred modes for carrying out my invention, it is to be understood that it may be practised in different ways falling within the broader spirit and scope of the invention, and accordingly I do not intend to be limited except as set forth in the following claims.

I claim:

1. Theprocess of coating a metal of thegroup consisting of molybdenum, tungsten, chromium, nickel, iron, cobalt, tantalum and manganese, and their alloys, with carbon which comprises treat,- ing the metal witha solution containing potassium permanganate and applying the carbon onto the treated surface.

and 'their alloys, which comprises treating the.

wire with a solution containing potassium permanganate, subjecting the treated wireto hydrochloric acid, further applying a solution containing potassium permanganate to the wire, then coating the wire with a carbon layer and heating the coated wire to bake the carbon thereon.

4. The-method of continuously recoating a car-- bon coated wire of the group consisting of tungsten, molybdenum, chromium, nickel, iron, cobalt, tantalum and manganese, and their alloys, which comprises treating the wire with a solution of potassium permanganate whereby. the previously of an oxidizing agent whereby a coating is formed on said wire of the reaction products of said oxidizing agent and said metal and then applying the graphite onto said coated surface. v

7. The method of coating a metal wire of, the

class of molybdenum, tungsten, chromium, nickel, iron, cobalt, tantalum and manganese, and their alloys, with a layer of graphite which comprises treating the wire with a solution of an oxidizing agent whereby is formed a coating of the reaction products of said oxidizing agentwith said metal, applying a layer of graphite onto the treated surface and baking the graphite layer onto the wire surface thereby forming on said surface a firmly adherent layer of carbon and said reaction products.

8. The method of coating the surface of a 7 metal body of the classconsisting of molybdenum,

tungsten, chromium, nickel, iron, cobalt, tantalum and manganese, and their alloys, with a layer of graphite, which comprises treating the metal with a solution of an oxidizing agent whereby the oxidizing agent reacts with the metal forming a coating thereon onto which the carbon adheres substantially better than onto the bare metallic surface, and then applying the'graphite onto the coated surface.

9. The method of coating the surface of a metal of the class consisting of molybdenum, tungsten, chromium, nickel, iron, cobalt, tantalum, and manganese, and their alloys, with a layer of graphite which-comprises treating the metal withan oxidizing solution which loosens particles on the metal surface, applying to the treated metal a cleansing agent which-does not appreciably react with the metal itself but removes the loosened particles therefrom, thereafter subjecting the metal to a solution of an oxidizing agent which reacts with the metal forming a coating thereon onto which the graphite adheres substantially better than onto the bare metallic surface and then applying the graphite onto the coated surface. 1

10. The method of continuously recoating a carbon coated wire of the class consisting of molybdenum, tungsten, chromium, nickel, iron,

cobalt, tantalum and manganese, and their alloys, with a layer of graphite which comprises treating the wire with a solution of an oxidizing agent and thenapplying another layer of graphite thereon.

11. The method of coating the surface of a metal body of the class consisting of molybdenum,

tungsten, chromium, nickel, iron, cobalt, tantalum and manganese, and their alloys, with a layer of graphite which comprises treating the metal with an oxidizing solution that forms a coating of the reaction products of said solutionand said metal and then applying the carbon onto the treated surface and baking said graphite into a firmly adhering layer with said coating,

forms a coating thereon onto which the carbon adheres substantially better than onto the bare metallic surface, applying a layer of the carbon onto the coated surface and baking the carbon layer thereon.

RUDOLF LOWIT. 

